Doom source code

The Doom source code was released December 23, 1997, initially under a not-for-profit license. Later, permission was granted to re-release the source code under the GNU on October 3, 1999.

Before release, the source code was tidied up by Bernd Kreimeier; the source release includes a changelog of his contributions. Several documentation files are also included. The original plan for the source code release involved a book Kreimeier was to write on the Doom engine; however, due to Doom's decreasing relevance in the gaming community, it was eventually judged not to be a marketable idea, and the project was abandoned. The source code was then released to the public.

Because of legal issues regarding the DMX sound library developed by Paul Radek which was used for Doom, the official release was of the source code to the port of Doom. The original source code for the DOS version remained unavailable until the 2023 Doom source code leak, when a copy of the DOS source code, as well as the source code for the Doom Macintosh version, surfaced online. The source code for Doom95 remains unavailable.

Many source ports were created in the wake of the source code release, starting with DOSDoom, released on the same day as the official source code release, which aimed to port the game back to DOS. Thus, the release of the source code allowed for the establishment of popular source ports such as Boom, ZDoom, Doom Legacy, Doomsday, EDGE and Vavoom, which greatly increased capabilities for modding the game.

Source code structure
The source code can be divided into sections. Files and functions within the source code have one- or two-letter prefixes to denote their subsystem.


 * AM_*
 * Automap code


 * D_*
 * Initialisation/general code


 * F_*
 * "Finale" (end of game) and "screen melt" code.


 * G_*
 * Main game loop/control


 * HU_*
 * Heads-up display


 * I_*
 * System-specific code


 * M_*
 * Miscellaneous (includes the menu)


 * P_*
 * Game logic/behaviour


 * R_*
 * Rendering engine


 * S_*
 * Sound code


 * ST_*
 * Status bar


 * V_*
 * General graphic rendering


 * WI_*
 * End-of level "intermission" screen


 * W_*
 * WAD file loading


 * Z_*
 * Zone memory allocation system

The following are common prefixes for functions, although they do not denote a particular subsystem, and there are no files with these prefixes:


 * A_*
 * Action functions invoked in sprite movement frames (these are the functions used in DeHackEd "code pointers")


 * PIT_*
 * Callback functions passed to P_BlockThingsIterator (see p_maputl.c)


 * T_*
 * "Thinker" functions set to be called each clock tic for some purpose (eg, moving platforms or flickering lights)

A detailed list of files and their purposes can be found in Doom source code files.

Doom Classic
Doom 3: BFG Edition incorporates the "Doom Classic" port allowing to play The Ultimate Doom and Doom II on 32- and 64-bit Windows, on the Xbox 360 and on the PlayStation 3. There are a few changes done to the source code and packaging here. Notably:
 * Bugs introduced in the LinuxDoom code by Bernd Kreimeier's cleanup and changes are absent
 * MUS2MIDI and TiMidity are incorporated for MIDI playback, instead of using DMX
 * A few static limits have been raised, notably visplanes and drawsegs to accommodate for No Rest for the Living's levels
 * Several #defines have been moved out of their original files and into either Precompiled.h or defs.h (both new files)
 * The Master Levels and No Rest for the Living are handled as mission packs like TNT: Evilution and Plutonia
 * The French language file is still present but emptied, French is removed from the language_t enum
 * The code is available under the GPLv3 or later

Note: this should not be confused with the iOS port also named Doom Classic.